Reflector-shade.



R. B. BENJAMIN.

REFLECTOR SHADE.

APPLICATION FILED DEC. 4, 1911.

Patented Sept. 10, 1912.

- UNITED STATES PATENT OFFICE.

REUBEN B. BENJAMIN, OF CHICAGO, ILLINOIS.

REFLECTOR-SHADE.

Specification of Letters Patent.

Patented Sept. 10, 1912.

Application filed December 4, 1911. Serial No. 663,968.

To all whom it may concern:

Be it known that I, REUBEN B. BENJAMIN,

a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented new and useful Improvements in ReflectorShades, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawing, forming a part of this specification.

My invention pertains to reflector shades, particularly such as used in connection with incandescent lamps.

It is the primary object of my invent-ion to provide a shade of this character which will distribute the light rays efiiciently and as evenly as possible over the required area.

the shade proper extends.

It 1s a further object of my invention to prevent, as much as possible, waste due to the rays extending outward at too wide an angle.

It is a further object of my invention to provide a shade'having the above characteristics which will accommodate either an ordinary bulb or a spherical bulb, at will.

A shade constructed in accordance with my invention is shown in the accompanying figure, the right hand ortion of which is a vertical section throug the shade, and the left handportion is a diagrammatic View showing the nature of the curves of the several surfaces of the shade.

Referrin now to the drawin 10 represents a suitable central supporting member for the shade, from the lower end of which The shade is formed so as to present three curved surfaces 11, 12 and 18, respectively, the curvature of which surfaces is determined in a manner hereinafter to be described.

14.- represents an ordinary bulb in the position which it will assume relatively to the shade, and the dotted line 15 represents a spherical lamp bulb in the same position.

16 indicates diagrammatically the lamp filament, the position of which will be approximately the same regardless of whether an ordinary bulb or spherical bulb be'employed. v

In describing the surfaces 11, 12 and 13 of the shade, we shall refer to the curvature of the lines of section of these surfaces, as shown when the shade is cut by a vertical plane passing through the axis of the shade, it being understood that the surfaces are figures of revolution, about the axis of the lamp-usually the center of the filament which point is taken as the basis of the calculations. This point may be termed the focal point.

In the drawings, a represents the focal point. It is also usual to decide upon an angle at which it is desired that the light shall be projected to the maximum extent, and the line passing through the focal oint at this angle may be termed the axis 0 distribution. In the drawings, 1) a b and a a 0 represent the axes of distribution, being incllned at an angle of 4 5 degrees from the vertical. It will be understood, of course, that the axes b a b and 0 a care, in reality, a part of a cone of distribution, but the axes are referred to separately for purposes of description.

Referring now to the right hand side of the figure: In order to determine the curvature of the surface 11, a point e is chosen upon theaxis c a 0, such point being placed at a sufiicient distance from the focal point a to allow room for the spherical bulb 15, and a parabolic curve, passing through the point e, is then described upon the axis 0 a c and having the focal-point a for its focus. The curved line d e f is thus obtained. In determining the curvature of the surface 12, a parabola passing through the point f, is described about the axis 7) a b and having its focus at the focal point a. The curved line 1 g is thus obtained. In determining the curvature of the surface 13, a parabola, having its focus at the focal point a, is described about the axis 0 a 0, so as to pass through the point 9, the curved line 9 72. being thus obtained. The surfaces 11, 12 and 13 are figures of revolution of the lines d e f, f g, and g h, respectively.

Referring now to the left hand side of the figure: a represent incident rays striking upward from the source of light, and impinging upon the surface 11; and k Z represent the reflected rays. The surface 11 being part of a parabola upon the axis 6 a b (it being understood that the axes b a b and c a c are reversed upon the left hand side of the figure), the reflected rays h Z will be projected in lines parallel with the axis of distribution b a b 2'. 6., in the embodiment shown, they will be reflected downward at an angle of 45 degrees, through the lamp bulb. a m represent an incident ray striking outward from the source of light and impinging upon the reflecting surface 12, and m, a designates the reflected ray. The surface 12 being part of a parabola upon the axis 0 a c, the reflected ray m n will be projected in a line parallel with the axis of distribution c a (2,- i. e., in the embodiment shown, the ray m n will be projected at an angle of 45 degrees downward. a 79 designates a ray striking outward from the source of light, and impinging upon the surface 12 at a part-thereof adjacent to the point at which it intersects the surface 13. p q designates the reflected ray which, as will be seen, strikes the surface 18 and is again reflected downward as at (I 1. a 8 indicates an incident ray striking outward from the source of light, and impinging upon the surface 13, s 6 being the reflected ray. The surface 13 being a portion of a parabola upon the axis 6 a b, the reflected ray .9 t will be projected in a line parallel with the axis of distribution b a b; 2'. e., in the embodiment illustrated, the ray 8 2. will be projected downward at an angle of 45 degrees.

The above description has related only to those rays which emanate from the focal point a. The filament is, however, of considerable length, and rays will of course issue from the whole length thereof. Such rays as do not emanate from the focal point a (for instance, such as issue from the to or bottom of the filament) do not follow the direction of the axes of distribution, but are reflected at different angles; as, for instance, the rays designated u o w and w '0 y. The result is that the light emanating from the filament is shed evenly over the surface to be illumined.

As will be seen from the above description, the surfaces of the shade are so cte-' signed that all the rays emanating from a predetermined focal point (with the exception of such rays as that designated a p which are reflected twice) are distributed downward in lines which are parallel with the predetermined axes of distribution; 71. (5., they are reflected at the predetermined angle, which, in the embodiment shown, is 45 degrees. The result is that a maximum number of the rays issuing from the lamp filament are reflected downward and outward in a predetermined cone of distribution, while rays issuing from other portions of the filament and the predetermined focal point, give an even distribution of light over the surface to be illumined.

The shade is such that it may be employed in connection with either a spherical globe or an ordinary pear-shaped globe, and the construction is such that this advantage is obtained with as little reflection of the rays back through the lamp as possible. It is further to be noted that waste owing to the extending outward of some of the rays attoo wide an angle is avoided; i. 0., the lamp is properly hoodedwhile keeping the shade within practical limits as to size.

Double reflection (as in the case of the ray a p is avoided to the greatest extent possible; and the rays are, in the majority of cases, reflected at a wide angle from the reflecting surface, absorption and diffusion of the reflecting rays being thereby minimized.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A reflector shade of a form which is a figure generated by the revolution, about the axis of the lamp to be used in the shade, of a line starting at a point at a predetermined distance from the axis of the lamp, said line extending outwardly and downwardly in a curve which approximately follows the curve of a spherical lamp contained in the shade, then following substantially the curve of a parabola drawn about an axis of distribution of the shade and having a determined point in the lamp filament for its focus, and then turning ownward for a predetermined distance.

2. A reflector shade of a form which is a figure generated by the revolution, about the axis of the lamp to be used in the shade, of a line starting at a point at a redetermined distance from the axis of t e lamp, said line extending outwardly and downwardly in a curve which approximately follows the curve of a spherical lamp contained in the shade, then following substantially the curve of a parabola drawn about an axis of distribution of the shade and having a determined point in the lamp filament for its focus, and then following substantially the curve of a parabola drawn about the other axis of distribution of the shade and having such point in the lamp filament for its focus.

3. A reflector shade of a form which is a figure generated by the revolution, about the axis of the lamp to be used in the shade, of a line starting at a point at a predetermined distance from the axis of the lamp, said line following substantially the curve of a parabola drawn about one axis of distribution of the shade and having a determined point in the lamp filament for 1ts focus, then following substantially the curve of a parabola drawn about the other axis of distribution of the shade and having such point in the lamp filament for its focus, and then turning downward for-a predetermined distance.

4. A reflector shade of a form which is a. figure generated by the revolution, about the axis of the lamp to be used in the shade, of

a line starting at a point at a predetermined distance from the axis of the lamp, said line following substantially the curve of a parabola drawn about one axis of distribution of the shade and having a determined point in the lamp filament for its focus, then following substantially the curve of a parabola drawn about the other axis of distribution of the shade and having such point in the lamp filament for its focus,

and then following substantially the curve witnesses. v

' REUBEN B. BENJAMIN.

Witnesses:

MABEL REYNOLDS, Manotmm'm Museum. 

